Hardware
Electrical characteristics
Board power voltages: 4.2 V
Output voltage max: +12 V
Output current max: 100 mA
Converting resistance tolerance: 0.1%
Channel series impedance: 165 Ohm
Temperature range: [0 °C, 85 °C]
Dimensions: 73.5 x 51 x 1.3 mm
Figure: 4-20 mA Board connected over Waspmote
If the 4-20 mA sensor is being powered from the 12 V sensor board supply, take into account that the series resistance used to measure the current on the current loop will produce a maximum voltage dropout of 3.5 V.
Connection diagram
The 4-20 mA Board for Waspmote has 4 input channels which allow the user to convert signals that come from 3rd party sensors or devices with this industrial standard. The 4-20 mA Board works with type 2, 3 and 4 current transmitters. Each channel can be configured for working with any of these types of connections: 2, 3 or 4:
When the jumper of one channel is connected, this channel is compatible with type 2 and type 3
If one jumper is moved away, this channel will be configured as float (type 4 connection)
Channel wiring for Plug & Sense!
The 4-20 mA board for Plug & Sense! has the same features as the Waspmote version. The four channels are accessible through the sensor sockets following this correspondence:
channel 1 → socket A
channel 2 → socket B
channel 3 → socket C
channel 4 → socket D
However, the transmitter categories cannot be modified on Plug & Sense! because the user has no access to the selection jumpers. Channels 1, 2 and 3 are predefined as type 2 or type 3, while channel 4 is type 4 only (its jumper is removed inside the enclosure).
Finally, each signal is wired following the next table.
Sensor connection on Plug & Sense!
Terminal box probe
To provide access to the board signals in the Waspmote Plug & Sense! encapsulated line, a waterproof terminal block junction box is provided as an accessory probe, making the connections on industrial environments or outdoor applications easier.
It consists of 2 cable glands and 6 terminal block connectors with screw. The junction box can be easily opened by removing the four external screws and the cover. Then, the user is able to make the necessary connections using the terminal block connectors. Finally, the cable glands should be adjusted and the junction box should be closed properly to avoid water ingress.
Please double check the terminal block connections to avoid wrong wirings or short circuits between poles. The Waspmote Plug & Sense! unit can be seriously damaged. Besides, ensure that the junction box is properly closed to avoid damage in outdoors applications. Libelium warranty will not cover damages caused by a wrong installation.
DB9 probe
The DB9 connector is commonly used in many applications with data transmission on industrial ambients. Libelium provides this probe as an accessory with a standard DB9 female connector and a cable with length of 1.5 meters.
Consumption
The consumption of the 4-20 mA Board depends on several factors. When the battery is fully charged, the consumption of the board is lower due to the DC-DC converter. This DC-DC converter rises the voltage from the battery voltage level to 12 V, so if the battery level decreases, the energy needed to maintain the 12 V level is higher. The nominal consumption of the board is 8 mA without sensor. Also, if the 4-20 mA Board is used to power other sensors, the consumption will increase.
Connectors
For connecting the 4-20 mA sensors, the 4-20 mA Board includes PTSM connectors. These connectors (PTSM from Phoenix Contact) allow to assemble the wires of the probe simply by pressing them into it. To remove the wire, press the slot above the input pin and pull off the wire softly.
Powering sensors from the 4-20 mA Board
The 4-20 mA Board includes a 12 V output that can be used as power supply for sensors. The majority of 4-20 mA sensor works in the 9-24 V range. Before connecting a sensor to the 4-20 mA Board, you must be sure that 12 V fits the sensor's range of the power supply. If you are going to use all channels, the consumption of the board will increase. It is important to know that the 4-20 mA Board is not designed to power industrial devices such as PLC's and thermostats: the maximum current output is about 180 mA.
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